You are pretty much exactly describing the recovery partition System76 released on Pop_OS 21.10.
I read through this discussion here. It’s an interesting idea and I can tell you have given it thought and fleshed out some of the details.
Not only does the ability to roll back with snapshots take care of probably 95% of cases where the recovery partition would be helpful, but keeping an up-to-date ISO on boot media has kind of already been established as a best practice on Garuda for the other 5% (or whatever). A lot of effort has been put in to get the Garuda Downloader to a state where it can be easily updated for this purpose.
I take your point that a flash drive can be easy to lose or whatever, but on the other hand it has other useful features that a recovery partition does not–you can use it to install Garuda onto a new machine, for example. There is also something to be said for the 4GB of SSD space not having to sit there doing basically nothing.
All that to say: I think it’s an idea with merit, but considering the tools Garuda already has in place the recovery partition might be a lot of work to solve a problem that doesn’t exist.